Embodiments of the present invention relate to methods for operating a compressor in case of failure of one or more measure signal, in order not to cause the antisurge controller to intervene by opening the antisurge valve, but, instead, to continue to operate the compressor, at the same time providing an adequate level of protection through a plurality of fallback strategies.
Anti-surge controller requires a plurality of field measures, acquired by the controller through a plurality of sensors and transmitters, to identify the compressor operative point position in the invariant compressor map. In case of failure, for example loss of communication between transmitter and controller, of a required measurement, operative point position is not evaluated. When this occurs, a worst case approach is commonly used to operate the compressor safely. With this approach, the failed measure is replaced by a value which permits to shift the operative point towards the surge line as safely as possible. For example, in compressor installations including a flow element at suction: in case of loss of the value of discharge pressure, the latter is substituted with the maximum possible value thereof, and in case of loss of the value of differential pressure in the flow element (h), the minimum possible value (i.e.: zero value) of such differential pressure is chosen.
In any case, this worst case approach tends to open the anti-surge valve, usually losing process availability even when this is not required by actual operating conditions.
It would be therefore desirable to provide an improved method which permits to safely operate a compressor and, at the same time, to avoid the above inconveniencies of the known prior arts.